The present invention relates to a positron emission tomography (PET) system, and more specifically, to a PET system for detecting positron emissions from a volume through a plurality of detecting elements arranged in a first two dimensional array about the volume, the first array being optically coupled to a plurality of light sensing members in a second two dimensional array so that a scintillation event created in a detecting element by a positron emission emanating from the volume is not necessarily identified as originating from an individual detecting element.
As is known, scintillation detectors used in nuclear medicine can be divided into two broad categories. The first category includes detectors which use one or a small number of large sized single scintillation crystals. The second category includes pixilated detectors employing a plurality of smaller sized crystals. In both categories, the detectors determine the position of a positron emission caused by decaying isotopes of a radioactive compound. The position of the positron emission is determined by calculating the locus of two oppositely directed gamma rays (i.e., 180xc2x0 apart) impinging the detectors and causing scintillation events within the crystals. In this way, xe2x80x9ccoincidentxe2x80x9d scintillation events identify a unique position of a positron emission. Typically, the radioactive compound is administered to a subject for rendering a tomographic image whereby the biochemical and physiological condition of the subject can be monitored by way of the detector.
Devices which fall into the first category are the PET detectors generally used with nuclear medicine gamma cameras now in general use. These detectors use large sized crystals, typically NaI(TI), coupled to a large number of photomultipliers (PMTs). Identification of the situs of the positron emission is determined by xe2x80x9cAngerxe2x80x9d logic. Thus, the position of the scintillation event is calculated by complex processing circuitry using the signals from several PMTs (anywhere from 3 to 95) and using a centroid finding technique to determine the situs of the positron emission.
The second category, includes detectors with small scintillation crystals known as pixelated detectors. Pixelated scintillation detectors consist of a large number of small sized crystals in which the locus of a gamma ray impinging upon the detector is calculated by identifying the individual crystal in which the event was converted to light (the scintillation process). These detectors typically use small (4 by 8 mm) BismuthGermanate (BGO) crystals. Typically the crystals are grouped such that their outputs are received by a particular group of PMT""s. Often referred to as xe2x80x9cblockxe2x80x9d detectors due to their block like structure, the rectangular array of crystals are coupled to a corresponding rectangular array of PMTS. In general, pixelated scintillation detectors determine a position for every scintillation event and the events which are not coincident are eliminated after the individual crystals are identified, as such the processing circuitry for pixelated detectors is likewise complex and the spatial resolution of the detector is limited to the size of the individual crystals.
Presently, a pixelated PET detector is desired which uses many small crystals, but does not require an alignment of the crystals and the PMTs for identifying a scintillation event by a specific crystal. Further a pixelated PET detector is desired in which the processing electronics can be simplified to determine the coincidence of the scintillation event first and then the position of the positron emission causing the coincident event.
Briefly stated, the present invention comprises a positron emission detection scanner. The scanner includes a first plurality of detecting elements arranged in a first two dimensional geometrical array, the detecting elements together defining a first detection surface oriented for receiving radiant energy stimulus incident thereto. The detecting elements each have a second surface for communication light from a scintillation event in response to receiving a radiant energy stimulus. A light transmitting member is provided for receiving light from the scintillation events from each of the detecting elements. A second plurality of light sensing members is arranged in a second two dimensional geometrical array, different from the first geometrical array. The alignment of the light sensing members is independent of the detecting elements, a predetermined group of light sensing members being responsive to light in the light transmitting member. The group of light sensing members collect the light from the light transmitting member and each one of the light sensing members of the group produce signals proportional to its respective portion of the collected light.
The present invention further comprises a positron emission scanner which includes a first plurality of detecting elements arranged in a first two dimensional geometrical array. The detecting elements together define a first detection surface oriented for receiving radiant energy stimulus incident thereto. The detecting elements each have a second surface for communicating light from a scintillation event in response to received energy stimulus. A light transmitting member is provided for receiving light from the scintillation events from each of the detecting elements. The light transmitting member has a detection surface and a transmission surface, the light transmitting member channeling light received by the detection surface by photon boundaries formed therein to distribute the light along photon paths such that the light is predictably distributed to exit the transmission surface. A second plurality of light sensing members is arranged in a second two dimensional geometrical array, the alignment of the light sensing members being independent of the detecting elements. In this manner, a predetermined group of light sensing members are responsive to light based on the distribution of the light in the light transmitting member and exiting the transmitting surface. The group of light sensing members collect the light from the light transmitting member transmission surface such that each one of the light sensing members of the group produces electrical signals proportional to a collected portion of the received light.
The present invention further comprises a positron emission scanner including a first plurality of detecting elements arranged in a first two dimensional geometrical array. The detecting elements together define a first detection surface oriented for receiving radiant energy stimulus incident thereto and the detecting elements each having a second surface for communicating light from a scintillation event in response to receiving a radiant energy stimulus. A light transmitting member is provided for receiving the light from the scintillation events from each of the detecting elements. The light transmitting member has a detection surface and a transmission surface. The light transmitting member channels light received by the detection surface by photo boundaries formed therein to distribute the light along photo paths such that the light is predictably distributed to exit the transmission surface. A second plurality of light sensing members is arranged in a second two dimensional geometrical array not aligned to the first array, and oriented toward the light transmitting member transmission surface. Each light sensing member collects light through the light transmitting member from one or more of the detecting elements and generates proportional electrical signals. A processor is provided for receiving the electrical signals from each of the light sensing members and for determining the position of the energy stimulus.
The present invention further comprises a method of determining the coincidence of a scintillation event. The method comprises the steps of detecting positron emissions from an area with an array of detecting elements in a first two dimensional geometric configuration; transferring light from scintillation events in the array of detecting elements resulting from the detection of the positron emissions to a channeling member; collecting light from the channeling member with an array of light sensing members in a second two dimensional geometric configuration, the alignment of the light sensing members being independent of the detecting elements with each light sensing member producing electrical signals proportional to the portion of light passing thereto; and processing the light sensing member signals to identify coincident scintillation events.